It is known that 3,5-dichloroaniline can be obtained, according to French Application No. 2,162,782, by a process for the dehalogenation of halogen-containing aromatic compounds which leads to the preferential production of deivatives carrying a smaller number of halogen atoms, at least one of which is located in the meta position relative to a functional group, in the vapour phase, by the action of hydrogen and in the presence of fixed-bed or fluid-bed catalysts, which is characterised in that aromatic amines containing several halogen atoms, or the corresponding nitro derivatives, ar brought into contact with hydrogen at a temperature of between 280.degree. and 420.degree. C., in the presence of a controlled-action hydrogenation catalyst such as a salt (chloride, oxide, nitrate, sulphate or chromite) of copper or of silver.
This process is characterised by its improved selectivity with respect to aromatic derivatives which are substituted in the meta position. However, experiment shows that, in particular when employing copper compounds on an alumina support, the process exhibits the major disadvantage that it requires frequent regeneration of the catalyst as a result of the formation in situ of carbon deposits due to the complete degradation of a little part of the starting derivatives.